High voltage fuse



Jan. 8, 1946. o. R. SCHURIG HIGH VOLTAGE FUSE Filed March 11, 1943 3Flu/5M5 l5 ELEMENT Inventor: Otto R. Schurig, y W 5! Y H if M |I|..k l41] V V u H m i is Attor' neg.

Patented Jan. 1946 HIGH VOLTAGE FUSE Otto R. Schnrig, Schenectady, N.Y., assignor to General Electric Company, a corporation of New YorkApplication March 11, 1943, Serial No. 478,785

2 Claims.

My invention relates to high voltage fuses, and more particularly, tohigh voltage fuses of the current limiting type.

The current limiting fuse functions by dissipation of'the fusibleelement throughout a fusible section of considerable length, asdistinguished from dissipation only at a point of reduced cross section,upon subjection of the fuse to excess currents of large magnitude. Ifthe diameter of the fuse wires is increased for applications wheretransient high currents must be passed without damage to the fusibleelements, then of course, the magnitude of the current at which meltingof the fusible element occurs is greatly increased. To afford protectionunder sustained overload current conditions whichjwould otherwise not besufficient to cause substantially instant fusing of the fusible elementand yet permit the passage without damage to the fusible elements oftransient overloads, other means must be provided.

It is an object of my invention to provide a new and improved currentlimiting fuse.

It is another object of my invention to provide a new and improvedcurrent limiting fuse which may be constructed for use at higher currentranges than was heretofore thought possible and which furthermore willgive complete protection on sustained overcurrents which would otherwisebe insufficient to cause fusing of the fusible element.

Further objects and advantages of my invention will become apparent asthe following description proceeds and the features of novelty whichcharacterize my invention will be pointed out with particularity in theclaims annexed to and forming a part of this specification.

For a better understanding of my invention reference may be had to theaccompanying drawing inwhich Fig. 1 is a view partly in section of acurrent limiting fuse embodying my invention; Fig. 2 is an enlarged viewof a portion of the fusible element of the fuse of Fig. 1; Fig. 3 is aperspective view of a portion of Fig. 2 to illustrate a modification ofmy invention; Fig. 4 is a view similar to Fig. 3 illustrating stillanother modification of my invention; and Fig. 5 is a sectional view ofa portion of a modification of the fuse of Fig. 1 to which my inventionis applied.

Referring now to the drawing, I have disclosed a tubular enclosingcasing I 0 which is constructed of glass, porcelain, or other suitableinsulating material. Metallic terminal ferrules II are securedrespectively on thebpposite ends of the casing by means of any suitableform of seal not shown. If the casing I0 is glass, 9. suitableglassto-metal seal will be provided. Within casing l0 there is suitablymounted anelongated'insulating support or core l2, composed of a highheatresisting ceramic or other suitable material. Core 12, which extendslongitudinally in casing III, is

of generally star-shaped construction in that it has a plurality oflongitudinally exte ding fins,

though the illustrated core 12 has four such fins, a core having morethan four fins may be employed depending upon the rating and size of theparticular fuse.

Core I2 serves to support a circuit interrupting element or conductor,generally indicated at It which in accordance with my inventioncomprises a plurality of serially arranged portions. The major portionof the conductor ll comprises one or more parallel arranged fusiblewires, or elements l5, which are constructed of a material such assilver and which are adapted to dissipate throughout a fusible sectionof considerable length as distinguished from dissipation only at a pointof reduced cross section upon subjection of the conductor H to excesscurrent of large magnitude. It should be understood, however, that theabove statement does not require instant dissipation throughout theentire length of wires it, but such wires may be constructed inaccordance with the teachings of United States Letters Patent2,157,907Lohausen, granted May 9, 1939, and assigned to the sameassignee as the present application.

Although we have shown two parallel wires, or fusible members IS in Fig.1, it should be understood that more than two such wires may beemployed, or only a single such wire as indicated in Fig. 5 may beemployed depending upon the current rating of the fuse. The reason forusing one or more fusible wires such as I5, is that it has been foundthat most effective current limiting action is produced when conductorsof very thin cross section are employed. Hence where the current ratingdemands a relatively large cross section, it is desirable to divide thistotal cross section into a number of parallel conductors having a thincross section such as a plurality of fine silver or zinc wires.

L In order to obtain operation of the fuse of .Fig. 1, on currents whichwill not cause melting of the fusible wires i5, I provide one or morethermal storage bodies such as are indicated at It which may be formedof copper or the like. As is best indicated in Fig. 2, the wires l 5maybe inserted in recesses or cavities I! each of which is filled with afusible conducting material such as is indicated at I8, preferablycomprising a low melting point solder of some sort, such as lead or tin,or alloys thereof. Although in Figs. 1 and 2 two thermal storage bodiesIt have been indicated, it should be understood that only one of thesethermal storage bodies may be used if desired. Upon moderate overloadcurrents, the wires l5 will begin to heat up and part of this heat willbe dissipated or absorbed by thermal storage body It. When this heat issuflicient to melt the fusible material It, an arc will be initiated beween wires l5 and body it, and interruption of the circuit will occurafter a time lag depending upon the magnitude of the overcurrent.

In Order to improve the operation, I preferably provide a resistorportion is interconnecting thermal storage body it as indicated in Figs.1 and 2. This resistor portion acts as a heater to control the timecurrent characteristic of the fuse link on moderate overload currents.As illustrated in Fig. 2 the resistor or heater section is may befastened to thermal storage body II by crimping, as generally indicatedat 20. It should be understood, however, that if desired, resistorsection is may be fastened to thermal storage body IS in the same mannerthat fuse wires I! are fastened thereto.

The conductor H, including the portions l5, l8 and i9, is serially woundon core l2 and the interior of easing I is filled with a granular inertarc-quenching material 2! such as fused quartz, or sand. By using astar-shaped core l2 as indicated in Fig. 1 the conductor l4 touches thecore only at spaced points so that the maximum length thereof is exposedto the inert granular filler material indicated at 2|. spirally windingthe interrupting element on core l2 permits the installation of anelement of relatively great length in a casing ill of practicaldimensions.

Instead of providing recesses i! in thermal storage body IS, the fusewires I! may be fastened thereto merely by a bead of solder such asindicated at 22 in Fig. 3, thereby providing separation of the wires l5from the thermal storage mass it. Also, if desired, the heater orresistor l9 may be fastened to thermal storage mass l6 by a bead 23 oflow melting point solder.

Under certain conditions, it may not be necessary to use a low meltingpoint solder and both the wires I5 and the heater or resistor portion iscan be fastened to thermal storage body l6 as by crimping, indicated at20 in Fig. 4.

In Fig. 5 I have shown my invention as applied to a current limitingfuse of the type disclosed in the copending joint application of GeorgeR. Serfilng and Carl L. schuck, Serial No. 410,382, filed September 11,1941, now Patent 2,337,937, and assigned to the same assignee as thepresent application. In current limiting fuses of the type disclosed andclaimed in that copending application, no supporting core for theconductor is provided. As illustrated in Fig.5, this fuse comprises acasing 24 filled with an inert granular arc-extinguishing material 25. Afusible element generally indicated at 26 comprises a major portion ofrelatively fine zinc or silver wire 21 which is serially arranged withthermal storage bodies 28 interconnected by a heater or resistor section29.

In the constructions described above the joints between wires l5 orresistor portion is and thermal storage body ii are designed to fuse ata substantially lower temperature than the wires 15. Upon applying anoverload current to the fuse illustrated in Fig. 1 which current is inthe neighborhood of two or three times the rated current of the currentlimiting fuse, each of the fuse wires l5 adjacent to the joint with thethermal storage body (8 raises the temperature of the joint, the mass ofthe member l6 providing the desired time lag in the heating of thejoint. When the melting temperature of the fusible portions l8 of Fig.2, or 22 or 23 of Fig. 3 is reached, separation of portions of conductorl4 occurs, initiating the interruption of the current flowingtherethrough. Only a single thermal storage body IS without heatersection I 9 may be employed, but by arranging the thermal storage bodiesin pairs separated-by a short length of heater wire or resistor wire,the time lag characteristic may be further increased. In the arrangementdisclosed in Fig. 1 the fusible joints are heated in part by the fusewiresand in part by the resistance wire which joins the two heat storagebodies.

when short circuit currents are applied to the fuse embodying myinvention, that is, currents in excess of the magnitudes ordinarilyencountered in overloads or transient inrush currents, the fuse wires i5dissipate substantially instantly to produce a high current limitingaction.

While I have disclosed certain particular embodiments of my invention,it will be apparent to those skilled in the art that my invention is notlimited to the particular constructions shown, but that changes andmodifications can be made without departing from the spirit and scope ofmy invention, and I therefore aim in the appended claims to cover allsuch changes and modifications.

What I claim as new and desire to secure by Letters Patent of the UnitedStates is:

1. In a high voltage fuse of the current limiting type, a casing, a pairof terminals one associated with each end of said casing, an inertgranular arc-extinguishing material in said casing, and a conductorembedded in said arc-extinguishing material interconnecting saidterminals comprising three serially connected portions including a firstportion adapted to dissipate throughout a fusible section ofconsiderable length as distinguished from dissipation only at a point ofreduced cross section upon subjection of said conductor to excesscurrent of large magnitude, a non-fusible thermal storage body ofsubstantial mass connected to said first portion and a third portionconnected to said body by means of low melting point solder including ashort rod of resistance material for heating said solder and melting thesame to interrupt the circuit upon moderate overcurrents which would notcause melting of said first portion, said serially connected portionsbeing arranged so that current flowing through said high voltage fusealso flows through said solder.

2. In a high voltage fuse of the current limiting type, a casing, a pairof terminals one associated with each end of said owing, a star-shapedinsulating support mounted in said casing, an inert granulararc-extinguishing material surrounding said support and a conductorspirally wound on said support interconnecting said terminals comprisinga plurality of serially connected portions including a first portionadaptedto dissipate throughout a fusible section of considerable lengthas distinguished from dissipation only at a point of reduced crosssection upon subjection of said conductor to excess current of largemagnitude, a pair of separated thermal storage bodies of substantialmass at least one of which is connected to said first portion, a thirdportion connected between said bodies, and means comprising a lowmelting point solder for uniting at least some of said portions, saidthird portion including a short length of resistance material forheating said solder and melting the same to interrupt the circuit uponmoderate overcurrents which would not cause melting of said firstportion, said serially connected portions being arranged so that currentflowing through said high voltage fuse also flows through said solder.

O'I'IQ R. SCHURIG.

